The present invention generally relates to welding and more particularly, to a welding torch employing a welding wire as a consumable electrode.
Commonly, when a consumable electrode is employed for a welding torch, electric current is fed to the electrode through a contact member held in contact with said electrode. In that case, a large amount of servicing of the welding torch has been required owing to the resultant severe abrasion or wear of the contact member. In order to cope with the problem as described above, there has conventionally been proposed an arrangement as shown, for example, in FIGS. 1 through 3.
More specifically, in the known welding torch in FIGS. 1 through 3, first and second abrasion-resistant guide members 3a and 3b are provided along an electrode passage in a torch body 1' so as to be spaced apart from each other. An abrasion resistant guide block 3c having a thickness smaller than the width of the electrode is provided at one side of the electrode passage between the guide members 3a and 3b. An electrode 25 is held between the guide block 3c and a contact member 7' having a thickness exceeding the width of the electrode. Electrode 25 is delivered while being fed with the electric current through the contact member 7', in order to perform the welding operation. Accordingly, the contact member 7' is merely formed with a deep groove as shown in FIG. 2 even if it is worn out. Thus welding operations may be performed without hindrance.
Incidentally, in an arc welding, the so-called stick phenomenon often takes place wherein the electrode tip adheres to an item to be welded (not shown) during arc starting or during welding. In this case, resistance heating represented by I.sup.2 R is produced in the electrode between the contact member 7' and the top of the electrode 25, i.e., between the current feeding position and welding position at the electrode tip. Thus, the electrode is extremely softened and therefore weak. In connection with the above, although the delivery of the electrode is arranged to be properly interrupted through detection, for example, of short-circuit current, the delivery of the electrode is seldom suspended immediately when the electrode tip has been fused onto the item to be welded. Namely, even after the electrode tip has been fused onto the item to be welded, the electrode in its extremely softened state is still delivered, to a certain extent, onto the items to be welded. In the above case, since the second abrasion-resistant guide member 3b is disposed adjacent electrode 25 between the end of the electrode 25 and the contact position between the contact member 7' and the end of electrode 25 as shown in FIG. 1, the extremely softened electrode section delivered towards guide member 3b is deformed by the member so as to create an enlarged section which resists further movement through the second abrasion resistant guide member. This so-called stick phenomenon, as shown in two-dotted chain lines in FIG. 3, prevents further feeding of the electrode in many cases. In such a case, it is a general practice to start the torch again after cutting off the electrode tip automatically or manually upon formation of the stick phenomenon. However, the electrode cannot be fed towards the item to be welded due to presence of the enlarged electrode section adjacent the entrance of the second abrasion-resistant guide member 3b as described above. Accordingly, it has been necessary for the operator to grasp the electrode tip with cutting pliers or the like and pull the electrode in the direction of X1 thereby drawing the enlarged electrode section through member 3b. However, since the space between the end of the welding torch and the item being welded is normally selected to be approximately 10 through 30 mm, the torch must be moved away from the item in the direction of X'2 a sufficient distance to allow removal of the seized electrode portion, thus resulting in inferior operability. Although sintered porcelain, which is superior in abrasion resistance and heat resistance, is normally used as the guide members, the mechanical strength of such sintered porcelain is not so high. Thus, there are cases where the guide members are damaged during forced removal of the seized electrode portion as described above, thus resulting not only in economic disadvantage, but the necessity of replacement of the guide member. Furthermore, in the arc welding operation using a consumable electrode, molten metal particles at high temperatures, i.e. the so-called sputter, are generally scattered. In a welding torch having such a construction as shown in FIG. 1 through FIG. 3, the sputter tends to enter through an opening or the like into the passage of the electrode wire or sliding groove portion of the contact member, so that delivery of the electrode wire or movement of the contact member may be interfered with. In the conventional welding torch as described above, a cover member may be used to prevent the sputter from entering the passage of the electrode wire and sliding groove portion of the contact member. However, in this case, it is difficult to manufacture a cover member to be applied to a narrow portion, thus requiring high manufacturing cost. In addition, even when the cover member is provided, maintenance of the torch tip end portion cannot be effected sufficiently, thus resulting in poor operability. Meanwhile, in the case where the so-called gas shielded arc welding is effected with the use of the conventional welding torch as described above, it is impossible to carry out welding in small spaces due to the large size at the forward end of the welding torch, with a difficulty in forming a passage for the shielding gas towards the item to be welded.